The lag between temperature and CO2. (Gore’s got it right.)

When I give talks about climate change, the question that comes up most frequently is this: “Doesn’t the relationship between CO2 and temperature in the ice core record show that temperature drives CO2, not the other way round?”

On the face of it, it sounds like a reasonable question. It is no surprise that it comes up because it is one of the most popular claims made by the global warming deniers. It got a particularly high profile airing a couple of weeks ago, when congressman Joe Barton brought it up to try to discredit Al Gore’s congressional testimony. Barton said:

In your movie, you display a timeline of temperature and compared to CO2 levels over a 600,000-year period as reconstructed from ice core samples. You indicate that this is conclusive proof of the link of increased CO2 emissions and global warming. A closer examination of these facts reveals something entirely different. I have an article from Science magazine which I will put into the record at the appropriate time that explains that historically, a rise in CO2 concentrations did not precede a rise in temperatures, but actually lagged temperature by 200 to 1,000 years. CO2 levels went up after the temperature rose. The temperature appears to drive CO2, not vice versa. On this point, Mr. Vice President, you’re not just off a little. You’re totally wrong.

Of course, those who’ve been paying attention will recognize that Gore is not wrong at all. This subject has been very well addressed in numerous places. Indeed, guest contributor Jeff Severinghaus addressed this in one of our very first RealClimate posts, way back in 2004. Still, the question does keep coming up, and Jeff recently received a letter asking about this. His exchange with the letter writer is reproduced in full at the end of this post. Below is my own take on the subject.

First of all, saying “historically” is misleading, because Barton is actually talking about CO2 changes on very long (glacial-interglacial) timescales. On historical timescales, CO2 has definitely led, not lagged, temperature. But in any case, it doesn’t really matter for the problem at hand (global warming). We know why CO2 is increasing now, and the direct radiative effects of CO2 on climate have been known for more than 100 years. In the absence of human intervention CO2 does rise and fall over time, due to exchanges of carbon among the biosphere, atmosphere, and ocean and, on the very longest timescales, the lithosphere (i.e. rocks, oil reservoirs, coal, carbonate rocks). The rates of those exchanges are now being completely overwhelmed by the rate at which we are extracting carbon from the latter set of reservoirs and converting it to atmospheric CO2. No discovery made with ice cores is going to change those basic facts.

Second, the idea that there might be a lag of CO2 concentrations behind temperature change (during glacial-interglacial climate changes) is hardly new to the climate science community. Indeed, Claude Lorius, Jim Hansen and others essentially predicted this finding fully 17 years ago, in a landmark paper that addressed the cause of temperature change observed in Antarctic ice core records, well before the data showed that CO2 might lag temperature. In that paper (Lorius et al., 1990), they say that:

changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing

What is being talked about here is influence of the seasonal radiative forcing change from the earth’s wobble around the sun (the well established Milankovitch theory of ice ages), combined with the positive feedback of ice sheet albedo (less ice = less reflection of sunlight = warmer temperatures) and greenhouse gas concentrations (higher temperatures lead to more CO2 leads to warmer temperatures). Thus, both CO2 and ice volume should lag temperature somewhat, depending on the characteristic response times of these different components of the climate system. Ice volume should lag temperature by about 10,000 years, due to the relatively long time period required to grow or shrink ice sheets. CO2 might well be expected to lag temperature by about 1000 years, which is the timescale we expect from changes in ocean circulation and the strength of the “carbon pump” (i.e. marine biological photosynthesis) that transfers carbon from the atmosphere to the deep ocean.

Several recent papers have indeed established that there is lag of CO2 behind temperature. We don’t really know the magnitude of that lag as well as Barton implies we do, because it is very challenging to put CO2 records from ice cores on the same timescale as temperature records from those same ice cores, due to the time delay in trapping the atmosphere as the snow is compressed into ice (the ice at any time will always be youngerolder than the gas bubbles it encloses, and the age difference is inherently uncertain). Still, the best published calculations do show values similar to those quoted by Barton (presumably, taken from this paper by Monnin et al. (2001), or this one by Caillon et al. (2003)). But the calculations can only be done well when the temperature change is large, notably at glacial terminations (the gradual change from cold glacial climate to warm interglacial climate). Importantly, it takes more than 5000 years for this change to occur, of which the lag is only a small fraction (indeed, one recently submitted paper I’m aware of suggests that the lag is even less than 200 years). So it is not as if the temperature increase has already ended when CO2 starts to rise. Rather, they go very much hand in hand, with the temperature continuing to rise as the the CO2 goes up. In other words, CO2 acts as an amplifier, just as Lorius, Hansen and colleagues suggested.

Now, it there is a minor criticism one might level at Gore for his treatment of this subject in the film (as we previously pointed out in our review). As it turns out though, correcting this would actually further strengthen Gore’s case, rather than weakening it. Here’s why:

The record of temperature shown in the ice core is not a global record. It is a record of local Antarctic temperature change. The rest of the globe does indeed parallel the polar changes closely, but the global mean temperature changes are smaller. While we don’t know precisely why the CO2 changes occur on long timescales, (the mechanisms are well understood; the details are not), we do know that explaining the magnitude of global temperature change requires including CO2. This is a critical point. We cannot explain the temperature observations without CO2. But CO2 does not explain all of the change, and the relationship between temperature and CO2 is therefore by no means linear. That is, a given amount of CO2 increase as measured in the ice cores need not necessarily correspond with a certain amount of temperature increase. Gore shows the strong parallel relationship between the temperature and CO2 data from the ice cores, and then illustrates where the CO2 is now (384 ppm), leaving the viewer’s eye to extrapolate the temperature curve upwards in parallel with the rising CO2. Gore doesn’t actually make the mistake of drawing the temperature curve, but the implication is obvious: temperatures are going to go up a lot. But as illustrated in the figure below, simply extrapolating this correlation forward in time puts the Antarctic temperature in the near future somewhere upwards of 10 degrees Celsius warmer than present — rather at the extreme end of the vast majority of projections (as we have discussed here).

Global average temperature is lower during glacial periods for two primary reasons:
1) there was only about 190 ppm CO2 in the atmosphere, and other major greenhouse gases (CH4 and N2O) were also lower
2) the earth surface was more reflective, due to the presence of lots of ice and snow on land, and lots more sea ice than today (that is, the albedo was higher).
As very nicely discussed by Jim Hansen in his recent Scientific American article, the second of these two influences is the larger, accounting for about 2/3 of the total radiative forcing. CO2 and other greenhouse gases account for the other 1/3. Again, this was all pretty well known in 1990, at the time of the Lorius et al. paper cited above.

What Gore should have done is extrapolated the temperature curve according this the appropriate scaling — with CO2 accounting for about 1/3 of the total change — instead of letting the audience do it by eye. Had he done so, he would have drawn a line that went up only 1/3 of the distance implied by the simple correlation with CO2 shown by the ice core record. This would have left the impression that equilibrium warming of Antarctica due to doubled CO2 concentrations should be about 3 °C, in very good agreement with what is predicted by the state-of-the-art climate models. (It is to be noted that the same models predict a significant delay until equilibrium is reached, due to the large heat capacity of the Southern ocean. This is in very good agreement with the data, which show very modest warming over Antarctica in the last 100 years). Then, if you scale the Antarctic temperature change to a global temperature change, then the global climate sensitivity to a doubling of CO2 becomes 2-3 degrees C, perfectly in line with the climate sensitivity given by IPCC (and known from Arrhenius’s calculations more than 100 years ago).

In summary, the ice core data in no way contradict our understanding of the relationship between CO2 and temperature, and there is nothing fundamentally wrong with what Gore says in the film. Indeed, Gore could have used the ice core data to make an additional and stronger point, which is that these data provide a nice independent test of climate sensitivity, which gives a result in excellent agreement with results from models.

A final point. In Barton’s criticism of Gore he also points out that CO2 has sometimes been much higher than it is at present. That is true. CO2 may have reached levels of 1000 parts per million (ppm) — perhaps much higher — at times in the distant geological past (e.g. the Eocene, about 55 million years ago). What Barton doesn’t bother to mention is that the earth was much much warmer at such times. In any case, more relevant is that CO2 has not gone above about 290 ppm any time in the last 650,000 years (at least), until the most recent increase, which is unequivocally due to human activities.

Below is the letter written to Jeff Severinghaus, and his response:

Dear Jeff,

I read your article “What does the lag of CO2 behind temperature in ice cores tell us about global warming?” You mention that CO2 does not initiate warmings, but may amplify warmings that are already underway. The obvious question comes up as to whether or not CO2 levels also lag periods when cooling begins after a warming cycle…even one of 5,000 years?

If CO2 levels on planet Earth also lag the cooling periods, then how can it be that CO2 levels are causally related to terrestrial heating periods at all? I am not sure what the ice core records are related the time response of CO2 to the cooling trends. If there is also a lag in CO2 levels behind a cooling period, then it appears that CO2 levels not only do not initiate warming periods but are also unrelated to the onset of cooling periods. It would appear that the actual CO2 levels are rather impotent as an amplifier either way…warming or cooling. We are talking about planet Earth after all and not Venus whose atmospheric pressure is many times larger than Earth’s.

If there is also a time lag upon the onset of cooling, then it appears that some other mechanism actually drives the temperature changes. So what is the time difference between CO2 levels during the onset of a cooling period at the end of a warming period and the time history of the temperature changes in the ice cores?

Dear John,

The coolings appear to be caused primarily and initially by increase in the Earth-Sun distance during northern hemisphere summer, due to changes in the Earth’s orbit. As the orbit is not round, but elliptical, sunshine is weaker during some parts of the year than others. This is the so-called Milankovitch hypothesis [this really should say “theory” — eric], which you may have heard about. Just as in the warmings, CO2 lags the coolings by a thousand years or so, in some cases as much as three thousand years.

But do not make the mistake of assuming that these warmings and coolings must have a single cause. It is well known that multiple factors are involved, including the change in planetary albedo, change in nitrous oxide concentration, change in methane concentration, and change in CO2 concentration. I know it is intellectually satisfying to identify a single cause for some observed phenomenon, but that unfortunately is not the way Nature works much of the time.

Nor is there any requirement that a single cause operate throughout the entire 5000 – year long warming trends, and the 70,000 year cooling trends.

Thus it is not logical to argue that, because CO2 does not cause the first thousand years or so of warming, nor the first thousand years of cooling, it cannot have caused part of the many thousands of years of warming in between.

Think of heart disease – one might be tempted to argue that a given heart patient’s condition was caused solely by the fact that he ate french fries for lunch every day for 30 years. But in fact his 10-year period of no exercise because of a desk job, in the middle of this interval, may have been a decisive influence. Just because a sedentary lifestyle did not cause the beginning of the plaque buildup, nor the end of the buildup, would you rule out a contributing causal role for sedentary lifestyle?

There is a rich literature on this topic. If you are truly interested, I urge you to read up.

The contribution of CO2 to the glacial-interglacial coolings and warmings amounts to about one-third of the full amplitude, about one-half if you include methane and nitrous oxide.

So one should not claim that greenhouse gases are the major cause of the ice ages. No credible scientist has argued that position (even though Al Gore implied as much in his movie). The fundamental driver has long been thought, and continues to be thought, to be the distribution of sunshine over the Earth’s surface as it is modified by orbital variations. This hypothesis was proposed by James Croll in the 19th century, mathematically refined by Milankovitch in the 1940s, and continues to pass numerous critical tests even today.

The greenhouse gases are best regarded as a biogeochemical feedback, initiated by the orbital variations, but then feeding back to amplify the warming once it is already underway. By the way, the lag of CO2 of about 1000 years corresponds rather closely to the expected time it takes to flush excess respiration-derived CO2 out of the deep ocean via natural ocean currents. So the lag is quite close to what would be expected, if CO2 were acting as a feedback.

The response time of methane and nitrous oxide to climate variations is measured in decades. So these feedbacks operate much faster.

The quantitative contribution of CO2 to the ice age cooling and warming is fully consistent with current understanding of CO2’s warming properties, as manifested in the IPCC’s projections of future warming of 3±1.5 C for a doubling of CO2 concentration. So there is no inconsistency between Milankovitch and current global warming.

87 Responses to “The lag between temperature and CO2. (Gore’s got it right.)”

Thanks for this clearly written post. The Antarctic ice core data is presently to the public very loosely, often in the interest of time or print space (I did so myself in a talk with high school students last week). It is important to remind everyone that i) we expect CO2 to lag behind temperature in ice core records, because of feedbacks, and ii)that the Antarctic cores are not a global temperature record.

We can predict a GLOBAL temperature within —– degrees based on 600,000 year old ice core samples.
And I am —- % confident in the accuracy of those GLOBAL temps.

[Response: These statements don’t make any sense and so can’t be filled in. -gavin]

[Further Response: Our estimates of the magnitude of future global warming do not come from ice core data, and do not depend on it in any way. The point of this post is that the ice core data are entirely consistent with what we already knew (and have known since 1896 A.D. when Arrhenius published his climate sensitivity calculations). The ice core data make a nice illustration, and do provide an independent test of climate sensitivity. That the ice core data do not change the answer demonstrates that there is not very likely anything missing in our understanding. One of the things that motivated this post was Congressman Barton’s use of ice core data to try to contradict more than 100 years of well established physics. But the data do no such thing.–eric]

Tom, is your objection that the ice core is 600000 years old, or do you object to the reconstruction of temperature based on deuterium? The latter technique is established and based on very reasonable physics. The former…? Well, is it your contention that D2O diffuses preferentially relative to H2O?
Or is it the fact that the ice cores were taken from a small geographic region. I don’t think the intent is to give “global” temperatures, but I trust the data locally to within, say 10-20%, and globally, I think it accurately portrays trends. This is born out by other techniques where we can cross correlate them.
It can be risky to assume that just because YOU don’t understand something, nobody else does either.

Tom appears challenged by the idea of building global climate models based on atmospheric physics and doing years of testing those models against actual data. Of course, no one is trying to make a prediction based on global ice core data. The ice core data are used in model validation.

[apologies up front for simplifying some things, but I think it is too easy to go in too much detail and miss the main points – though the devil is often in the details…]

Historically, before human intervention, changes in CO2 lagged temperature rises – accepted fact. But the CO2 rising does enhance the effect of rising temperature – a positive feedback. The warmer it is, the more CO2 released into the atmosphere, which makes it get warmer still – a basic positive feedback system.

In itself I dont think the positive feedback can be disputed as it is just based on the effect of CO2 on solar radiation coming in and radiation from the earth going back out. Never mind the historic record – a simple lab experiment can prove the feedback effect.

What may happen is that other feedbacks balance this out on some timescale or another, but that doesn’t change the fact that atmospheric CO2 and other greenhouses cause a positive feedback effect.

When we increase CO2 artifically we are simulating that positive feedback, and it has just the same effect – ie it gets warmer. The fact that the climate record shows a strong correlation between temperature and CO2 certainly seems to tell us that the balancing effects don’t add up to enough to prevent the changes, because if they did, then the climate wouldn’t have oscillated like it did.

I just read the comments on coyoteblog about this and had to reply there becuase such an incomplete picture was presented – but thought I’d add my reply here too, for folks who don’t follow that blog:

There seems to be an assumption in that thread that a positive feedback is just that – a positive feedback that keeps on forever being positive.

There are many examples in nature of positive feedbacks that die out.

– Set fire to a forest. It starts from a cold forest, then add a small flame, it grows to a huge forest fire, burns out, goes out, goes cold. Few years later the whole thing repeats.

– Population growth – algae blooms – they start small, they grow almost exponentially, run out of food, die off.

– Spread of a disease in a population – the more people have it, the more they infect, until it burns itself out.

The same thing happens with CO2 and temperature. The positive feedback starts up, gets worse, until eventually it hits a stabilisation.

In the case of our climate it could be as simple as it is only very marginally positive, so our extra help is enough to put it into a growth mode when combined with the increase in solar influx. Take away either and that is enough to kill the positive feedback.

Or it could be that eventually it gets so hot that we become a shiny ball of cloud which cools down rapidly.

The whole of the last several million years has been a classic two state climate, oscillating between ice ages and warm periods, with sudden changes between the two. That is undisputed by anyone on any side of the debate. That is exactly the sort of situation that would be caused by having positive feedback to switch from cold to warm, and eventually a negative feedback to switch fom warm to cold.

In geological time, the balance of the system has changed several times, and just like any system can have a resonance at certain points, the climate can reach a resonant point where it is teetering between two states (our current 100,000 year ice age warm period cycle). Eventually the contintents shift or the sun changes and things settle down into a long warm or cold period.

If you look at our climate, and compare it to a machine that has a vibration problem, you hear the vibration build up and then die away, build up and die away – the big build up and die away is the hundreds of millions of years climate shift, and the individual vibrations that make up the fine grain are the 100k year switches between ice age and warm spell. Of course, in the climate case, the whole thing is bounded by the creation of the solar system and the sun going poof and is definitely not cyclic in the billions of years timescale. Maybe someone can think of a better analogy?

What we have right now (in my view) is an opportunity to actually control things and prevent both the positive feedback being enough to lead to rapid temperature growth, and the negative feedback being enough to cause an ice age. At least for the time being, when the continents, orbits and solar situation mean it is so finely balanced. In longer timescales, we will have to adapt, but for the next few million years its finely balanced and we can keep it just where we want it.

If people would stop bickering about it and misrepresenting the situation in either direction and look at the bigger picture then we might actually start constructively planning the climate for our future.

What if the oceans are being warmed due to another forcing? How is GHG warming the oceans AT THE OBSERVED RATE? How do the models account for this? Do the models predict the rate of ocean warming we are seeing? Do the models use field measurements to verify assumptions regarding heat transfer between air and ocean?

I noticed that JA Smith, in a comment on this subject on this site said that heating of the oceans by GHG was expected to take decades to centuries, yet it seems to be showing up now. The mechanism of IR radiation heating the ocean through the skin seems very slow, much slower than observed.

The reason I think that this is important is that if some other mechanism is heating the oceans, then wouldn’t they be expected to outgas CO2?

I know that Solanki says that he has bounded solar forcings a something like .5 watts/m^2, but how does he do this? Does he extrapolate a couple of decades worth of satelite oberservations over centuries?

Is cloud formation well understood? Isn’t it possible that even minor variation if solar output could affect cloud formation, would this not greatly amplify any effect, even if the variations were minor?

How is it known that the cosmic ray theory is untrue?

[Response: …Sigh… We’ve addressed all of these questions elsewhere on this site. –eric]

An unanswered question is that 55 millon years ago CO2 levels reached 1000ppm. According to many predictions in the media those levels of CO2 should have caused a runaway greenhouse effect. Though the climate then was considerably warmer than today this did not happen, otherwise we would not be here. Can somebody explain this?

Hello to the respected scientists at RealClimate. Congratulations on your efforts! This site brings good understanding of the current status of climate science in a clear way, understandable by the laymen like me.

There is still plenty of misunderstanding and confusion about the scientific findings on the climate science, promoted by some people. I am hoping that your research and explanations reach further in the minds of the masses by perhaps writing a book or airing a documentary made by scientists; as the skeptic side has done, but mostly by misleading and inaccurate arguments.

A recent published paper states that “phase relationship between CO2 and EDC temperature inferred at the start of the last deglaciation (lag of CO2 by 800±600 yr) is overestimated and that the CO2 increase could well have been in phase or slightly leading the temperature increase at EDC.”

[Response:I haven’t read that paper yet but it’ll be interesting to look at. I’ll be very surprised if it turns out that CO2 leads global temperature after all, but it could certainly lead Antarctic temperature. Yet the evidence published to date — for the few intervals of time where one can actually do the calculation accurately, show that CO2 does lag Antarctic temperature — refer to the papers cited in the post –eric]

Ok, so you come up with ONE POSSIBLE explanation for the temp/co2 lag. A much simpler and logical explanation is that temperature controls co2 concentration.

[Response: Temperature does have an influence on CO2 concentration. Indeed, about 1/5 of the glacial interglacial change in CO2 can be explained by the greater solubility of CO2 in cold ocean water. So what? That doesn’t change the fact that if you burn fossil fuels you put CO2 into the atmosphere, regardless of what temperature does (or would do) on its own. Why do people find this so difficult to comprehend? It is not complicated!–eric]

Regardless, we are now in a position where co2 levels and temperatures are rising. Using your logic, the following is happening:

– C02 concentrations have risen from about 290 to 380 ppmv in the last 100 years.
– Since co2 levels were otherwise constant, the entire 90 ppmv rise is due to man’s burning of fossil fuels. The Mona Loa co2 record shows a smooth constant rise of co2 in the atmosphere, as one would expect from an accumulation resulting from the burning of fossil fuels.
– For this buildup of c02 in the atmosphere to occur over the 100 year time frame, the residence time of co2 must be between at least 50 and 200 years. Essentially once emitted, co2 in the atmosphere is almost permanent. Even though the relationship between co2 in air and dissolved in fluid is well known, and dozens of independent calculations of residence time center around a 5 to 6 year residence time.
– Mass balance calculations, however, indicate that co2 concentrations should be twice as high as they are given the known emissions and the long residence time, indicating a missing sink. It is postulated that the ocean is a major carbon sink, absorbing most of the missing 50 percent of the co2. Somehow, at the same time, co2 is both stable in the atmosphere for hundreds of years and 50 percent of the co2 emitted each year is absorbed by the ocean.

An alternative explanation is that temperature controls co2. Using this logic, the following is happening:

– Temperatures rise naturally, warming the oceans.
– Warmer oceans release co2 into the atmosphere, raising its concentration in the air.
– Co2 released to the atmosphere through the burning of fossil fuels is cycled through the oceans based on a five year residence time, so that only about a quarter of the co2 in the atmosphere at any one time is from man.
– A close review of the Mona Loa data indicate substantial fluctuations in the incremental annual increase in co2. For the 50-year record, annual increases vary from as low as 0.25 to as high as 2.70 ppmv. The co2 levels do not increase on a steady basis, say at a rate corresponding the growth in the world economy.http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_mm_mlo.dat

– There is a strong (qualitative) correlation between ocean surface temperature and the increase in atmospheric co2. After relatively cooler ocean surface years, the increase is small, and after relatively warmer ocean surface years, the increase is large. The relative annual increase in co2 mirrors ocean surface temperatures.http://www.ncdc.noaa.gov/oa/climate/research/2007/mar/global.html#Temp

– Therefore, it appears that temperature (of the ocean) does in fact control co2 concentrations in the atmosphere

[Response:Much of what you say may sound sensible, but it isn’t. There is *zero* question about the cause of the recent CO2 rise, as we’ve explained multiple occasions (e.g. here). One of the things pointed out in that post is that we know that the rise in atmospheric CO2 is entirely caused by fossil fuel burning and deforestation because many independent observations show that the carbon content has also increased in the ocean. If the oceans had contributed to the rise in atmospheric CO2, it would hold less carbon. There is no surprise that the CO2 in the atmosphere winds up partially in the oceans, nor that the amount of CO2 going into or coming out of the oceans varies in time and space — that’s simple equilibrium chemistry between the liquid (that is, dissolved) and gaseous phases, and does explain part of the variability about the long term rising trend. So what? That doesn’t change anything!–eric]

If people would stop bickering about it and misrepresenting the situation in either direction and look at the bigger picture then we might actually start constructively planning the climate for our future.

I agree, we are presented with a golden opportunity for global planetary engineering. If we pin atmospheric carbon dioxide concentration to right about 300 to 320 ppm, we are looking at 20-30 thousand years of stable climate, with huge fresh water reserves, and we are only about half way into a global mass extinction.

The entire system indeed appears to still be salvageable IF WE START RIGHT NOW!

“Q: Is the rising CO2 level the cause of global warming or the result of it?

Ball: That’s a very good question because in the theory the claim is that if CO2 goes up, temperature will go up. The ice core record of the last 420,000 years shows exactly the opposite. It shows that the temperature changes before the CO2. So the fundamental assumption of the theory is wrong. That means the theory is wrong. … “

You know, as a physicist, I really have trouble letting go of conservation of energy. I mean if temperatures are rising, what is the source of all that energy. It has to come from somewhere, right. We know it’s not the Sun–not enough change there. Let me know when you have a theory that is consistent with at least the basic laws of physics.
Likewise, if the carbon is coming from the oceans, then why is it depleted in C-14. Are you proposing it stays put in the oceans for tens of thousands of years? There are LOTS of other inconsistencies in your little theory, but I’ll stop there. Come back when you’ve worked those out.

Post #7 (B Buckner): So, let me get this straight, you are seriously proposing that by pure coincidence the levels of CO2 started rising naturally over the last 100 years or so to levels not nearly seen in at least 650,000 years…and probably for millions of years? And, that just coincidently, the rate of the rise has consistently been (when averaged over a few year period to smooth out variability due to seasonal cycles and other factors) equal to about half of the emissions of CO2 that we are putting into the atmosphere?

And…this isn’t even mentioning the isotopic evidence.

[Response: I think he is proposing just that. Not a little bizarre, but I’ve heard it before. It is getting quite boring to hear it over and over again, particularly when we’ve addressed it no less than three times here at RealClimate. To paraphrase someone else, just because you can say something that sounds like science doesn’t make it science (or true). –eric]

The more I read Real Climate, the less convinced I am of the underlying hypotheses that form the AGW assumptions. There is a Temp/CO2 lag throughout the entire periodic cycle (even at cooling)? Why is there a methane correlation as well (that isn’t explained by a dependence on temperature)? Is there a delay in the methane concentrations as well? Where can I find a simplified description of the feedback equations that model such a system?

[Response: The methane correlation is because natural methane emissions are also affected by climate – principally from wetlands. They increase in wet and warm conditions and decrease when it is cold and dry. These changes combined with the shorter residence time for methane in the atmosphere mean that the lag is much less (a few years or so). In fact, methane reacts so quickly and in both hemispheres almost simultaneously that its variations are used to tie the together the ice core records in Greenland and Antarctica. But as with CO2, those lags are related to the climate effect on sources and don’t have anything to do with the GHG effect on climate which is known from lab measurements and direct observations. – gavin]

Most importantly, why are the tropospheric temperatures not changing at the modeled rate?

I read your explanations for some of these fundamental questions, and they make sense – but they are only hypotheses – where are your testable predictions and experimentally derived results? Please don’t answer with models! Models can be made to verify any results – but validation is another matter.

Eric,
Another great post. Like most people who comment on this site I have had arguments about this issue with contrarians.
But there is one issue that I need clarified: the fraction of warming or cooling caused by CO2.
In one paragraph you say that it is 1/3 but in the next you say that CO2 and other greenhouse gases amount to about 1/3. Jeff Severinghaus in his letter says that CO2 and other greenhouse gases amount to about 1/2.
Thanks for this great site.

[Response:The exact amount depends on the magnitude of other changes, which aren’t certain. In his Sci. Amer. article, Hansen estimates that the radiative forcing from all greenhouse gases together (glacial-interglacial) is -2.6 +/- 0.5 W/m^2, and ice sheet albedo is -3.5 +/-1 W/m^2. So the greenhouse gases together (excluding the water vapor feedback) account for 0.3 to 0.55 of the total. CO2 is roughly half of the total greenhouse gas change, so thats 0.15 to 0.26. Note that part of the uncertainy in all this is the time uncertainty — from the ice core records, we can pick a rather precise time and look at a rather precise number for greenhouse gas concentrations, but pinning down the magnitude albedo change at exactly the same time (since albedo is not globally uniform, obviously) is impossible. –eric]

Don’t bother to quibble with Coyote over the cause. The important issue is whether we are going to get the climate under control and survive or not get the climate under control and die attempting to breathe hydrogen sulfide. It seems that hydrogen sulfide from overheated oceans is implicated in the end-permian event and at least one other extinction. The question is what levers do we have to push the climate away from a hydrogen sulfide catastrophe? Regulating carbon dioxide is one of those levers and maybe the only one of those levers within relatively easy reach.

I love realclimate for its deep understanding of climate issues that people like myself cannot get anywhere else. It is like having your own personal scientist at your disposal whenever it is needed.

For instance I am currently still remonstrating with some people on another forum about the hockey stick data and realclimates insights into it have been invauable.

I have read all of the arguments about climate change and lets get it clear. Relative to 1750 greenhouse gases are now higher by 150 ppmv and in addition to this the world is warming. What lags what might seem like a good debate to have and one that has to be answered to as the skeptics for good scientists to set up sites like this to argue the cause but come on the evidence is clear, it is not the SUN that has caused the current warming and we have a perfectly robust argument for stating that it is greenhouse gases (all of which has increased).

Case closed for me, however as we rely on fossil fuels for everything you can understand the reticence for doing anything about it but that is what Governments are for, to make tough choices and to limit our freedoms when necessary.

I beg the world for R&D of a magnitude not seem since the second world war but the world is slow to respond unfortunately.

Thank you both Eric and Jeff for a clear explanation of a difficult issue.

I’ve only recently stumbled across RealClimate and it’s a breath of fresh air to find climate scientists endeavoring to make the science of climate change accessible to the public. Unfortunately most of the “accessible” (read superficially plausible) material I have encountered to date is from skeptics.

I was aware of Milankovitch cycles and their role in driving ice ages and so I was somewhat confused by Al Gore’s implicit attribution of global temperature changes to CO2 in An Inconvenient Truth. Another quibble I had was that Gore presents the impact of sea level rise without referring to the long time scales (in human terms) involved. (Although recent data from Greenland and Antarctica suggest that these timescales may not be as long as the IPCC says.)

However, on reflection I think Gore’s approach is apposite. Scientists are guarded and reticent by nature and training. Carefully qualified statements on the probability that climate change is real and anthropogenic, along with possible potential impacts – also carefully qualified and filled with jargon – are lost on the general public, who would find even the simplified approach of RealClimate overwhelming.

On the other hand, politicians speak with absolute conviction even when telling the most outlandish lies. In fact, the art of persuasion in the real world (think advertising) is far removed from that in the scientific world. In contrast to most politicians and many sceptics, Gore is reasonably careful with the truth. However, he is aware that leadership requires forceful persuasion and clearly articulated conviction about the correct path. Consider the difference between, “If we don’t reduce our use of fossil fuels we can kiss our way of life goodbye”, and “I think the balance of evidence suggests we reduce CO2 emissions or there is potential for serious consequences.”

A final point. The fact that CO2 lags temperature during cooling and warming periods in the last 600,000 years means that it does not initiate these changes. This means that the current warming trend is qualitatively different from those we can study through ice cores etc., even if past warming was amplified by a CO2 feedback. Past warmings are not an analogue for our present situation, which to my mind places a greater burden of proof on climate scientists regarding evidence for climate change.

Not only does CO2 lag the temperature changes in the ice age, but the CO2 feedback is only capable of explaining 20% to 40% of the total temperature change and, in many timelines, the temperature trends and the CO2 trends are going in the opposite direction.

These are facts that should be studied and understood versus downplayed or ignored.

[Response: These are facts that are studied and indeed understanding the details of the glacial-interglacial CO2 changes ranks as one of the great challenges in the field of paleoclimatology. It has not means been entirely solved. Prior to human activities interveneing, the CO2 and temperature have often been going in opposite directions because there is a lot else going on, and that continues to be the case. The well known cooling due to Pinatubo in 1992 is a case in point. But as greenhouse gases increase — at many many times the rate than they have int the past — they become the dominant forcing, and the other causes of temperature change become decreasingly relevant. If you are riding your bicycle, there is a myriad of things that might make you fall over — hitting a rock, wobbling because you’re tires are flat, looking distractedly at a cute member of the opposite sex. If a car runs you over, those minor forcings become pretty irrelevant. The point is that we are essentially (rather literally) running over the climate system with a car.–eric]

Eric,
Your response to #11 begs the question if the oceans are adding CO2, does that offset the missing 50 percent of CO2 that should be in the atmosphere due to the Mass Balance Calculations for 50-200 year residency of CO2. Also, I would like to know how this fits in with the Modeler’s use of buffers to explain why the oceans do not recycle the CO2 in the atmosphere.
You state in the response to #10, “…There is no surprise that the CO2 in the atmosphere winds up partially in the oceans, nor that the amount of CO2 going into or coming out of the oceans varies in time and space — that’s simple equilibrium chemistry between the liquid (that is, dissolved) and gaseous phases…”
Are the buffers a part of simple equilibrium chemistry, and where can I go to read up on this and how it pertains to the Models.

[Response: You could start with virtually any basic undergraduate textbook on the carbon cycle. For example, The Earth System by Lee R. Kump et al., Prentice Hall, 2nd Edition, 2003, 419 pages. –eric]

I mean if temperatures are rising, what is the source of all that energy. It has to come from somewhere, right. We know it’s not the Sun–not enough change there.

No, the energy does come from the Sun. Not because the Sun has changed its brightness, but because the ability of the enormous flow of solar energy through the Earth’s surface environment to escape back to space has been impaired.

I’m curious about the use of the Pinatubo eruption in testing the climate models. Their success in modeling the effect of the eruption is brought up quite frequently. What else is used to assess their efficacy? I imagine the modelers are all waiting with baited breath for the next big eruption, but in the meantime, what else is of particular use in this regard. I heard a retired professor on the radio recently going on about how the models are being tweaked so that they agree with each other and so they aren’t independent and aren’t tested like real scientific theories are. That seemed like a totally implausible assertion to me. I would have thought that you were trying to make them agree with reality rather than each other. Given that, what aspects of the climate system in particular are used for testing in the absence of volcanic pyrotechnics.

[Response: Lots of the things! Response to El Nino events, the 20th century trends, the mid-Holocene (6kyr ago), the 8.2kyr event, the last glacial maximum, ozone depletion, North Atlantic Oscillation, the Sahel drought…etc. These are all (in some sense) a response to forcings and so allow us to test exactly the aspects that will be important in the future. The models are not tuned to these events (most ‘tweaking’ is done to match the climatologies, seasonal cycles and diurnal cycles instead) and so they provide a good validation of the models. – gavin]

Eric says “If you are riding your bicycle, there is a myriad of things that might make you fall over — hitting a rock, wobbling because you’re tires are flat, looking distractedly at a cute member of the opposite sex. If a car runs you over, those minor forcings become pretty irrelevant. The point is that we are essentially (rather literally) running over the climate system with a car.”

Now that sir is a good analogy (even if some will doubtless disagree).

Eric: thank you for your thoughtful response. I would be interested in seeing data indicating that ocean levels of carbon are increasing over time. I have been unable to find such a data set, so any help would be appreciated. I am skeptical that such comprehensive data can exist given the size and depth of the ocean. Also, seeing as the oceans contain 50 times the co2 of atmosphere, and the huge exchange that occurs between ocean and atmosphere, I would think such an increase would be trivial and difficult to document.

[Response:You are right that this is a non-trivial calculation, but there is a huge literature on this. Much of the work is based on carbon isotope studies. You might start with the web site of the Carbon Dioxide Information Analysis Center. –eric]

Ray Ladbury: Your theory on the co2 temp lag is that temperatures stop falling and then rise for some unknown reason, in an environment of low and falling co2 concentrations. After 5000 years of rising temperatures and 4200 years of rising co2 concentrations, temperatures reverse themselves in an environment of high and rising co2 concentrations and start falling for some unknown reason. It seems you have a few things to work out yourself.

And now we can get on to the more serious implications of CO2 & CH4 lagging warming. Re #7, while permanent venusian-style runaway warming is not possible now (until the sun becomes a lot hotter in billions of years), we could go into (what scientists have told me) is hysteresis, a really great warming for even up to 100,000 or 200,000 years, in which a lot of life dies out, before the world cools back down again.

We humans could be pulling the trigger on that right now, and who knows when we might reach a point at which even if we cease & desist from our human emissions, the positive feedback chain of “warming causing emissions causing more warming” takes on a life of its own. Maybe in 10 years, maybe in 100 years, maybe in 200 years.

Maybe we’re in this hysteresis phase already, and in 2058 scientists will be able to definitively say that on April 29th, 2003 at 3:20 pm (well, science does improve over time) the world passed the tipping point into this hysteresis period, and if only people had listened to Earth Day suggestions back in 1990, and put forth all effort to implement them, we could have avoided it.

This hysteresis may not be a high probability, but it is a possibility, since it happened 55 & 251 mya, so we laypersons need to keep our sights trained on that, and do all we can to prevent it from happening.

That CO2 lags (& is caused by) warming is no consolation to me whatsoever. It make the whole thing a lot more dangerous.

The Royal Society (the national academy of science of the UK) produced a very readable report in 2005 titled Ocean acidification due to increasing atmospheric carbon dioxide it includes very clear explanations of the science, both that relating to levels and how they have and are changing, and the likely impact on marine ecosystems. It has informative graphics and references to the most important papers and datasets up to that time. You could take this as your starting point in hunting down the actual raw data.

Re #26 Testing the models:

Thanks Gavin. I suspected that the answer was going to be along those lines. This would make for a worthwhile article some time in the future. Especially given the never-ending skepticism about the validity of climate models.

Re #30
I’m puzzled by two points.
1) Figure 1 in the report you cite states that atmospheric residence times for CO2 are 3 years, which seems at odds with the stated residence times of 50-200 years elsewhere in this blog (and from many other sources).
2)It has also always puzzled (Figure 1 again) me that the anthropogenic fluxes of CO2 are approx 6Gt/yr or only 5% of the terrestrial biological fluxes to and from the atmosphere and 6% of those to/from the surface ocean. It’s amazing such a tiny perturbation can have such a huge impact of atmospheric CO2 and climate (yes I realise the maths adds up). It makes me wonder whether we can be confident that reducing the burning of fossil fuels will restore the balance, or could it be that large scale anthropogenic land use changes are more important than fossil fuels.

[Response: Fossil fuels are the main problem but land use changes are a non trival part of it (something like 20%). The residence time calculation is confusing and indeed the concept of residence time is not very useful for a multicomopnent system. The average CO2 molecule does spend only a few years in the atmosphere, giving that 2-3 year residence time you cite. But effective residence time is much longer because of the equlibrium (or near equlibrium) between surface ocean and atmosphere and biosphere and atmosphere. The residence time of a CO2 molecule in the surface ocean is nearly as short as in the atmosphere, so many of the molecules that go in come right back out! So the effectie residence time of the combined system is what is important, and that is more onthe order of hundreds of years — or indeed, thousands, if we are talking about the residence time inthe combined surface ocean/atmophere/biosphere, vs. the deep ocean.–eric]

I would propose that the lag of CO2 behind temperature is simply an artifact of the measurement technique. Hand waving arguments about dynamics of feedback etc. are unnecessary. Here is an electrical engineer’s take on it.

The temperature record is inferred from hydrogen/deuterium ratios in the ice itself. The H2 is “trapped” instantaneously as the snow is deposited. Thus the signal instantaneously follows temperature.

The CO2 is determined from analysis of ice bubbles. Formation of ice bubble is not instantaneous. How long does it take to form a bubble? It depends, since it is controlled by depths and pressures. In the websites from the Siple and Vostok sites you can find that it takes 60-80 meters for the snow (fern) to be compressed to form ice which has bubbles trapped. They alsa say that below 3000m, the pressure is so great that the bubbles are crushed.

This implies that the resolution of the ice core C02 time series is related to the length of the record. Long records necessarily have low resolution because you need to have a low accumulation rate to get only 3000m in 400,00 to 600,000 yr. The Siple site has a resolution of 22 years because the accumulation rate is high. However the record only goes back 200 years for the same reason. THERE CAN BE NO UNIVERSAL TRAP TIME. It depends onthe particular site ( i.e. on the snowfall rate at that site).

60m / 3000m * 600kyr = 12000 yrs to trap a bubble! This is an extreme over estimation, however, because the fern is compressed as it is buried. However 500 to 1000 years (the delays seen between the CO2 and temperature) would not be out of the question. This is much longer than the C02 time constant (100 to 200yr).

The signal from the CO2 is therefore passed through a moving average filter. Think about the response of moving average to a step function. The output is a ramp with a duration of the integration time. Compared to the input, the output looks delayed. You can imagine any input as composed of a series of small steps, so the output would resemble the input, just a little delayed, and with any “spikes” averaged down. The technical method is to convolve the input with a square pulse. As the pulse with goes to zero, we have a delta function, and the output is an exact copy of the input with no delay. This is the case for the hydrogen/deuterium ratio.

Conclusions:

1) Ice bubble CO2 must necessarily show some lage behind the temperature from hydrogen/deuterium in the ice itself.

2) The CO2 signal is also low pass filtered by a MA filter with this same integration time. This integration time appears to beseveral times longer than the residence time of a CO2 perturbation in the atmosphere.

Dave Dougherty

[Response: David, this is all quite reasonable, but be careful not to reinvent the wheel. What you’ve said is encapulated in my short statement that there is uncertainty in the lag/lead precisely because of uncertainty in the trapping time, which does (as you say) vary with conditions (notably, temperature and snow accumulation rate). Lots of work has gone into getting this sorted out in detail, and the Monnin and Caillon papers I cited in my post are the examples of such work — and that work shows a lag AFTER correcting for the trapping time. Read those papers, you will like them! –eric]

# 19 Edward wrote [It seems that hydrogen sulfide [H2S] from overheated oceans is implicated in the end-permian event and at least one other extinction]

I don’t want to step on anyone’s current unpublished research, so I have to tread very lightly. This is being actively investigated for the current human-caused global warming scenario with models and paleoclimate data. So far, results indicate that H2S extinction is not one of our biggest worries.

So far, results indicate that H2S extinction is not one of our biggest worries.

Since our current atmospheric carbon dioxide rise is unprecedented in geological history, short of a major asteroid impact, I would suggest otherwise. Clearly we need to stop and reverse the trend before the end of the century. Apollo 13 needed to stop and reverse the trend before the end of the mission.

If you want to boil this post down to its bones and get past the (necessary) scientific language…This is an extremely oversimplified (and scientifically and PC incorrect) explanation… but here it is:

Natural warming is a three step process between temperature and CO2 where everything “causes” everything else.

1) The Earth’s temperatures increase a little due to Earth’s orbit changes.

2) This little warming causes the oceans to warm up which releases huge amounts of CO2.

3) The increased CO2 now causes a huge temperature increase- like adding billions of tiny suns to our solar system(physics).

Now that you have a basis for understanding, go and read the original post.

(Fourthly, I duck as every researcher takes a well-deserved strong swing at me for being [correctly] way too inaccurate, muddying the situation and butchering science and reality…but you get a glimmer of understanding for the first time.)

[Response: No need to duck. That’s really it in a nutshell. Thanks for the clarity! We scientists sometimes lose sight of the essentials because the details are ultimately imporant, and of course are interesting to us. (I do hasten to add that it isn’t as simple as the oceans warming alone resulting in more CO2. There’s also ocean circulation and chemistry changes, both probably more important than the temperature.)–eric]

Pleeeease (esp the hosts here) comment on the following (which was passed onto me from my parish priest, who refuses to say anything about GW); he simply doesn’t believe anything I have to say on the topic:

VATICAN CITY, APRIL 27, 2007 (Zenit.org).- Scientists might not have human behavior to blame for global warming, according to the president of the World Federation of Scientists.

Antonio Zichichi, who is also a retired professor of advanced physics at the University of Bologna, made this assertion today in an address delivered to an international congress sponsored by the Pontifical Council for Justice and Peace.

The conference, which ends today, is examining “Climate Change and
Development.”

Zichichi pointed out that human activity has less than a 10% impact on the environment.

He also cited that models used by the Intergovernmental Panel on Climate
Change (IPCC) are incoherent and invalid from a scientific point of view. The U.N. commission was founded in 1988 to evaluate the risk of climate change brought on by humans.

Zichichi, who is also member of the Pontifical Academy of Sciences, showed that the mathematical models used by the IPCC do not correspond to the criteria of the scientific method.

He said that the IPCC used “the method of ‘forcing’ to arrive at their
conclusions that human activity produces meteorological variations.”

The physicist affirmed that on the basis of actual scientific fact “it is not possible to exclude the idea that climate changes can be due to natural causes,” and that it is plausible that “man is not to blame.”

To that end, Zichichi explained how the motor of meteorology depends on
natural phenomena. He gave as an example the “energy sent by the sun and
volcanic activity that spits out lava and enormous quantities of substances in the atmosphere.”

He also reminded those present that 500,000 years ago the Earth lost the
North and South Poles four times. The poles disappeared and reformed four times, he said.

Zichichi said that in the end he is not convinced that global warming is
caused by the increase of emissions of “greenhouse gases” produced through human activity.

Climate changes, he said, depend in a significant way on the fluctuation of cosmic rays.

[Response: I’m afraid I don’t know what to say. Most of what these guys say is incoherent (we lost the N and S pole!??). The few coherent things are wrong. –eric]

[Response:Wikipedia has a bio on him. I participated in a workshop in Cicily organized by Zichichi (under the auspices of the WFS) several years ago. Needless to say, I was quite disappointed with Zichichi’s penchant for making brazen assertions in areas of science (such as climate modeling) where he is transparently ignorant. Sadly, this is just more of the same old from Zichichi. -mike]

# 35 Thomas wrote: [Since our current atmospheric carbon dioxide rise is unprecedented in geological history, short of a major asteroid impact, I would suggest otherwise].

Now, I am niggling. However, have you recently talked to publishing scientists who are actively researching hydrogen sulfide (H2S) poisoning?

I have- last month..it’s where I work… and this is what they had to say.

This does *not* mean that hydrogen sulfide poisoning is a dead issue.

It does not mean that human-caused global warming is not potentially dangerous…just read the published body of research since 1842…or better yet talk to research scientists who are actively publishing in this like I talk to them weekly.

Bottom line…many I talk to are scared. They (publishing scientists) use words even publicly such as “the evidence is alarming to me” based on the body of published research since 1842.

This is about the most forceful that they are allowed to be. Some of them privately state to me that they think it might already be too late to stop extreme damage…maybe even to our civilization, but we still have to try.

But I am not going to back down from the H2S evidence even if the evidence is currently saying something that people disagree with or is not alarming enough for them.

However, you are right to question me on what I am saying, because it is not published yet in an open matter. I post from two IP adresses…one of them will tell you what you want to know.

B. Buckner. Gee. You got all that from a post in which I said butkis about the cause of warming or cooling. My “theory” on the current warming epoch is consistent with the scientific consensus and with the evidence. Look, warming won’t just happen. There needs to be an energy source that is increasing. What is yours?
As to the question of where the CO2 comes from, that is also unambiguous–it is mainly from anthropogenic burning of fossil fuels with significant contributions from other anthropogenic activities.
As to the oceans, they are indeed large. The question is how much CO2 gets transported to the depths (where it would indeed be difficult to sample it) and how much stays near the surface. Best evidence is that the oceans remain a net carbon sink.

A trivial correction — despite widespread popular misuse, especially among sportscasters, “literally” doesn’t mean “metaphorically or in an analogy.” That would be “figuratively.” “Literally” means the thing physically happens. If we were literally running over the climate system in a car, Detroit would have produced a car thousands of miles long, probably with its own measurable gravitational pull and perhaps its own atmosphere.

[Response: You are running a risk discussing language with me, son of a professor of English and grandson of a strict grammarian! In any case, I was using “literally” figuratively. So there!–eric]]

The 100ppm drop in CO2 is not, primarily due to colder oceans. The following is an explanation of why colder oceans alone can not account for a 100 ppm drop in CO2. (This as summary from the paper. See paper for details).

As there is a vast amount of fresh water in the glacial period, in the new ice sheets, the ocean becomes Salter (3%). Salter water can hold less carbon dioxide (6.5 ppm less for a 3% increase in salt content). Colder water can hold more carbon dioxide, however, the deep ocean is already an average of 4C and will freeze (salty or not) at around -1.8C. The estimated maximum drop deep in deep ocean temperature is 2.5 C. The surface subtropical oceans were estimated to have cooled by about 5C. (Note vast areas of the high latitude oceans were covered by ice, during the coldest period and could hence no longer absorb carbon dioxide.)

The reduction in carbon dioxide, due to colder oceans, is estimated to be max. 30 ppm. Now as vast areas of land which are currently forested, were covered by the glacial period ice sheets, the temperate forest is no longer using carbon dioxide which adds carbon dioxide to the atmosphere. In addition, during the glacial period large sections of tropical rain forest changes to savannah (About a third of the tropical forest changes to savannah. The planet is drier when it is colder), as savannah is less productive that tropical forests that change also adds carbon dioxide to the atmosphere. The Nature article estimates the temperate forest change and the increase in savannah, adds 15 ppm of carbon dioxide to the atmosphere.

As there is 100 ppm to explain the above are not the solution. The above article explains that increased biological production in the ocean, due iron and phosphate in the dust is hypothesized to cause an increase in the biological production in regions of the earthâ��s ocean which are currently almost lifeless due to a lack of nutrients.

Re #39 (cce): He must be, because the ice sure didn’t disappear. Ice, magnetism, whatever. Maybe there’s a solar connection! :( Jim Hansen is probably right that guys like this will go to their grave spouting the same nonsense.

Re #33 (Dave D.): Ice core measurement issues aside, remember that there has to be some degree of lag because a) the initial warming is from Milankovitch changes, not CO2, and 2) the delayed turnover of ocean water means that not all the CO2 will outgas in a short period of time.

I don’t want to step on anyone’s current unpublished research, so I have to tread very lightly. This is being actively investigated for the current human-caused global warming scenario with models and paleoclimate data. So far, results indicate that H2S extinction is not one of our biggest worries.

Has someone found a new, better and more ghastly way of killing off 95% of all life on earth – and perhaps us as well – so that fungus may once again reign supreme – but you can’t tell us what it is as of yet?

Perhaps more important than what Zichichi thinks, is what the Catholic church as a whole, and the pope in particular, think on the subject. Advancing that understanding was the purpose of this conference. Please note that in the article you posted there is no reference to any other speaker or the conclusions of the conference. It’s just coverage of a skeptic’s views.

Have a look at the following article, found on http://www.climateark.org, with coverage of the conference and the Catholic Church’s rapidly increasing attention to climate change and the environment in general.

Two myths propagated in this thread. First the ice cores do not show a maximum of 300ppm CO2 or anything like that. There are very few data points for the interglacial peaks before the present one and CO2 spikes like the present one would not show up. The second myth is that the extra CO2 is “entirely” manmade. The thread here http://www.realclimate.org/index.php?p=87 that makes that claim does not show that quantitatively (e.g. does not take into account natural variations in carbon isotope ratios). However, there is certainly plenty of qualitative evidence that much of the current CO2 spike is anthropogenic. As for coincidence, modern man spread across the planet about 60k years ago, but didn’t get beyond hunter-gatherer stage until the present interglacial period. The current CO2 spike is likely to be mostly fossil fuel, but could be partly coincidence. The last century is more likely to be natural coincidence rather than CO2 warming and aerosol cooling (another coincidence?).

[Response:[No, no, and no. We’ve been through this many times before. As I wrote to another “skeptic” that kept harping on this issue: The point is that more is being produced by humans than is winding up in the atmosphere and this is what we expect to happen. Sure, it is possible that not “all atmospheric increases are anthropogenic.” I never claimed otherwise. But to suggest that the natural environment has arbitrarily decided to start increasing the flux of CO2 into the atmosphere, right around the same time we are doing it is bizarre. Let me turn this around: what is the evidence that would suggest this is happening, and why? As for the aerosols and CO2 going up at the same time, umm. THINK man, THINK!–eric]

Here’s a link showing one way carbon isotope ratios can vary naturally. http://adsabs.harvard.edu/abs/1996GeoRL..23..371K shows vegetation changing its amount of CO2 it holds (Ci/Ca) based on natural climate changes.[

[Response: This is a nice paper. Yes of course 13C of the atmosphere varies naturally. I never suggested otherwise. One of the things that is clear is that 13C of the trees is now more negative than in the last 400 years. This is just one of the two million, five hundred thousand, one hundred and twenty five bits of evidence is support of the obvious fact that CO2 is going up because humans are putting it there. –eric]

What’s worrying is that positive feed-forward carbon cycle effects have the potential to reduce the effects of any attempts to limit fossil fuel CO2 emissions.

The lack of understanding of these issues shouldn’t be reassuring. One example is the global soil reservoir of organic carbon (which is not a single ‘pool’, but which is made up of many components, some which are very labile (rapid turnover via microbial and root respiration) and some of which are very long-lived (humic material). Estimates are that microbial respiration will speed up as the soil warms, resulting in a net flux of CO2 to the atmosphere.

Another is the permafrost reservoir, which is smaller than the active soil pool, but which is similar in size to the atmospheric carbon pool. The permafrost has been melting, and soil temperatures from boreholes are on an accelerating upward trend. That’s another source of CO2 that is responding to the warming temperatures.

Then you have the terrestrial vegetation pool, which is the most active. The claim that CO2 immediately increases plant growth and acts as a fertilizer is a highly oversimplified argument, since plant carbon uptake is dependent on water, temperature, and nitrogen suppy. The amount of carbon stored as vegetation is similar to the amount in the atmosphere as CO2.

The historical glacial-to-interglacial transition effects can also be seen in what is happening to the Arctic sea ice. As summer sea ice in the Arctic decreases, the snow/ice cover changes to open ocean, the amount of sunlight that is reflected drops from 80-90% to about 20%. Not only that, but the sea ice insulates the atmosphere from the ocean, and without it heat fluxes from the ocean to the atmosphere increase – all of which assists in the melting of the permafrost. Similar effects are certain to occur with Antarctic sea ice as well – it’s just a question of the heat content of the Southern Ocean and the buffering ability of the Antarctic ice sheet.

The 8.2 kyr Holocene thermal maximum is thought to have been buffered by the presence of the Laurentide ice sheet in the northern hemisphere. However, there wasn’t a massive increase in CO2 at that time. The critical factor is probably the rate of increase in heat content of the Southern Ocean, and the ability of the massive heat sink of Antarctica to absorb this. As for the Arctic, it seems that it’s already over the ‘tipping point’ and the changes there will not be reversible.